Method of Mixing and Extruding Viscous Materials and Gearbox for Dispensing the Same

ABSTRACT

The present invention relates to a method of mixing and dispensing viscous materials, comprising the steps of: inserting a cartridge containing one or more viscous materials in a chamber; activating a first motor ( 1 ) to move a plunger from a first position to a second position within the cartridge and activating a second motor ( 2 ) to move the plunger from the second position further within the cartridge to dispense the material.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to a method of mixing and extruding viscousmaterials, particularly relatively highly viscous or pasty materials,and to a gearbox, in particular to a superimposing gear drive, fortransmitting high torque and/or high revolutions per minute to an outputdrive shaft without changing gears. The gearbox may particularly be usedtogether with dispensing cartridges and mixer elements for mixing anddispensing multi-component dental impression materials.

2. Description of the Related Art

Dispensing devices with cartridges are often used in the field ofdentistry for mixing and dispensing dental compositions of two or morecomponents, such as impression materials, restoratives, adhesives,cements, etching gels, sealants and the like.

In one type of dispensing device that comprises an applicator and acartridge, the applicator has a plunger that is advanced either manuallyby the user or automatically by a machine during a dispensing operation.Often, the plunger is received in an open end of the cartridge and bearsagainst a piston within the cartridge. As the plunger is advanced tomove the piston, the piston expels or dispenses a quantity of materialthrough a front outlet opening of the cartridge.

The dispensing cartridge of such a device often comprises twocompartments that are formed by two cylindrical bodies arranged inparallel to each other. Each compartment contains a specific component,usually either a base paste or a catalyst paste. These two componentsare pressed from their respective compartments out into a mixing area,or tip, where the components mix to form the required dental material.The pressure further urges the mixture out of the mixing tip so that thedental professional can use it as desired.

One type of such dispensing devices is an assembly (e.g., the Garant™dispenser available from 3M ESPE AG) that includes a reusable,hand-operated applicator and a disposable cartridge. Another type ofsuch dispensing device is an automatic dispensing system (e.g.,Pentamix™ 2 available from 3M ESPE AG) that includes a motor-drivenmixing unit and reusable and interchangeable cartridges. The mixing unitcomprises a chamber for holding the cartridge, and two parallel,motor-driven plungers designed to plunge into two respectivecompartments of the cartridge and to exert high pressure on the viscouscomponents contained therein. The motor drive for the plungers provideshigh torque to extrude the viscous or highly viscous components underhigh pressure into a mixing tip. Furthermore, the motor also provides areasonably higher speed to rapidly move the plungers forward andbackward within the cartridge when the viscous components are not beingextruded. DC motors are generally used in such devices. For example, themotor drives the plungers into a first or “back” position for fillingnew components into the cartridge and/or inserting new cartridges ofcomponents into the machine. After refilling, the plungers are driveninto a second or “initial” position, wherein the plungers are in director indirect contact with the component(s). When the plungers eachcontact a component, the resistance, and therefore the load, to thedrive increases and a high load is applied to the driving gearbox andmotor during the dispensing operation.

It is difficult to achieve both high torque at low speed, and also lowtorque at high speed, without changing gears. It is also difficult toachieve highly different speeds, e.g., differing by a magnitude of 100,using a linear drive of any kind without changing gears or usingclutch-like devices. The changing of gears typically requires acomplicated drive. Furthermore, it is very difficult or sometimes evenimpossible to change gears under load. Devices that can perform thesefunctions can as a result be complicated and expensive.

Furthermore, highly viscous, multi-component mixtures, like dentalimpression materials, are produced using mixing devices in which theindividual components of the mixture are simultaneously supplied fromseparate cartridge cylinders to a mixer. From the mixing area, themixture is then dispensed from a front end. The mixer may be a staticmixer or, preferably, a dynamic mixer having a rotary mixer element.Known dynamic mixers have at their rear end (inlet side) a centralhexagonal opening for coupling to a drive shaft, which shaft rotates themixer element of the mixer, and the drive shaft is preferably connectedto a motor. Accordingly, it is desirable to use a drive unit which candrive also the dynamic mixer in addition to moving the plungers.

It would be desirable to overcome these and/or other disadvantages ofknown gearboxes and methods of mixing and extruding viscous materials.

SUMMARY OF THE INVENTION

The gearbox according to the invention is adapted to be driven by atleast two motors (hereinafter the first motor and the second motor,respectively, although additional motors are not excluded). The gearboxcomprises a first output drive shaft, wherein the first output driveshaft provides at least two different driving speeds; hereinafterreferred as the lower and higher speeds. The higher speed is preferablyin the range of from 30 to 200 times faster than the lower speed, andmore preferably in the range of from 80 to 120 times faster than thelower speed. Even more preferably the higher speed is at least 100 timesfaster than the lower speed. Driving the plunger with the lower speedmay result in a standard dispensing speed of 22.5 mm/min. This resultsin a plunger speed of 2.250 m/min when the motor is driven at a higherspeed with a speed transformation ratio of 100, as mentioned above. Itmay be provided that the dispensing speed is about two times thestandard dispensing speed, i.e., 45 mm/min or any other value in-betweensuch as 33 mm/min. During the lower speed a normal load is usuallyapplied when extruding the materials and during the higher speed a loadis applied which is generally just needed to move the plunger withoutpushing against the materials. The first output drive shaft can bedriven by the first motor and/or by the second motor to provide the atleast two different speeds. Furthermore, if the first output drive shaftis driven by the first and second motor at the same time, the outputdrive shaft speed will be the sum or the difference of the two drivingspeeds of the motors, depending on the ratios of the gears of thegearbox and the rotation directions of the motors. For example, if thegearbox has a first transmission ratio between the speeds of the firstoutput drive shaft and the first motor with the second motor standingstill, and a second transmission ratio between the speeds of the firstoutput drive shaft and the second motor with the first motor standingstill, then the first output drive shaft speed is the sum (or thedifference, depending on the rotation directions of the motors) of afirst transmitted speed of the first motor and a second transmittedspeed of the second motor. In this case the first and second transmittedspeeds are the products of the first or second transmission ratios andthe first or second motor speeds, respectively. Each motor may be avariable-speed motor or a constant-speed motor. Thus, it may be providedthat the two motors are permanently connected with the output driveshaft via the gearbox. In case that only one motor is driven, i.e. oneinput shaft is rotating the other motor prevents the second input shaftfrom rotating such that a force can be transmitted from the first inputshaft to the output shaft.

The gearbox of the invention preferably comprises a superimposing geardrive. Examples of useful superimposing gear drives include bevel geardrives, differential gear drives and planetary gear drives.

A superimposing gear drive comprises, in principle, at least threedifferent kinds or groups of gears or gear wheels, which are hereinafterreferred to as the first gear/gear wheel, second gear/gear wheel andthird gear/gear wheel. The third gear is arranged in engagement with thefirst and second gear wherein a carrier preferably carries the thirdgear. In case of a planetary gear drive the first, second and third gearwould correspond to the inner gear, outer gear and planetary gear,respectively. In the planetary gear drive the carrier is hereinafteralso referred as planet carrier. Typically, a planetary gear drivecomprises at least one planetary gear, and preferably a plurality ofplanetary gears that may be connected to each other by a planet carrier.The planetary (third) gears are arranged in engagement with the innergear and the outer gear. The inner (first) gear, the outer (second) gearand the planet carrier may be connected to a drive connection whichcould be either a input drive connection or an output drive connection.

The superimposing gear drive of the present invention uses two driveconnections as input drives, each connected to a motor, and one driveconnection is connected to a first output drive shaft. The torque andthe speed of the two input drive connections are superimposed in thesuperimposing gear drive. The three kinds or groups of gears of thesuperimposing gear drive, as discussed above, are movable. A variableoutput speed at the first output drive shaft is obtained by vectoriallyadding or subtracting the speeds provided by the first and secondmotors.

The embodiment of a planetary gear drive comprises at least an innerplanetary gear often called sun gear, an outer planetary gear which iscalled the annulus gear or ring gear and at least one planet gear,wherein a planet carrier supports at least one planet gear. Therefore,the planetary gear drive provides at least three drive connections, onein connection to the inner gear, one in connection to the outer gear andone in connection to the planet carrier. In the embodiment of a bevelgear, most of the gears/gear wheels are beveled and the inner gear mayhave the same size or a similar shape as the outer gear.

According to a first aspect of the invention, a gearbox is adapted to bedriven by at least a first motor and a second motor and comprises atleast a first output drive shaft. The gearbox is adapted to drive thefirst output drive shaft with a higher torque when driven with thesecond motor than when driven with the first motor. Moreover the gearboxis adapted to drive the first output drive shaft with a higher speed ormore revolutions per minute when driven with the first motor than whendriven with the second motor.

It may be provided that the speed of the first output drive shaft is thesum or difference of the first motor and the second motor.

Preferably the drive connections of the first gear and the second gearare selected as the two input drive connections, which are connected toa second motor and to a first motor, respectively. The drive connectionof the carrier is selected as the first output drive shaft whichprovides different speeds and different torques according to the twomotors which drive the gearbox at the two input drive connections. Thesecond motor is adapted to drive the first gear, and the first motor isadapted to drive the second gear. Due to the different gear transmissionratios from the first motor and the second motor to the carrier andtherefore to the first output drive shaft, the first output drive shaftis driven to provide high torque, by driving the first gear of the geardrive with the second motor. On the other hand, when high revolutionsper minute are needed and less torque is sufficient, the second gear isdriven by the first motor, which provides higher revolutions per minuteat the first output drive shaft.

According to a second aspect of the invention, the drive connections ofthe carrier and the second gear are selected as the two input driveconnections. The drive connection of the carrier is connected to thesecond motor and the drive connection of the second gear is connected tothe first motor. The first output drive shaft is connected to the firstgear and provides different speeds and different torques according tothe two motors which drive the gearbox at the two input driveconnections. The second motor is adapted to drive the carrier and thefirst motor is adapted to drive the second gear. Due to the differentgear transmission ratios, the first output drive shaft is driven toprovide high torque, by driving the carrier of the gearbox with thesecond motor. On the other hand, when high revolutions per minute areneeded and less torque is sufficient, the second gear is driven by thefirst motor, which provides higher revolutions per minute at the firstoutput drive shaft.

According to a third aspect, the gearbox of the invention provides afurther speed at a second output drive shaft, which may be differentfrom the two other speeds, without changing gears and without anadditional motor. This second output drive shaft may be used to drive anadditional mixing element. The second drive shaft has preferably a fixedspeed ratio relative to the first output drive shaft and/or to thesecond motor, i.e. the speed of the second drive shaft is proportionalto the speed of the first output drive shaft and/or to the speed of thesecond motor. Preferably, the driving of the mixing element is onlyneeded (and used) when the plunger is advanced for dispensing the pastematerial. It is further preferred that the mixing speed is adjusted inaccordance with the output speed of the highly viscous materials whichis dependent on the advancing speed of the plunger. The second outputdrive shaft is thus only rotating when the second motor drives the firstoutput drive shaft. This can be achieved by a direct connection of thesecond output drive shaft to the output of the second motor. The secondoutput drive shaft provides preferably 200 to 700 revolutions perminute, but can be designed for any speed appropriate to the material(s)being mixed.

The invention preferably provides a gearbox with high torque at lowspeed, e.g. for pressing out the components, and high speed atrelatively low torque which are provided at an output drive shaft, e.g.for rapid positioning the plungers, without using a clutch and withoutchanging gears.

The invention provides the further advantage that both high torque atlow speed and high speed with relatively low torque are provided at afirst output drive shaft, and a third speed is provided at a secondoutput drive shaft, without using a clutch and without changing gears.This is enabled by the use of a superimposing gear drive providing apermanent connection between the first output drive shaft and two motorsas well as a permanent connection between the second motor and thesecond output drive shaft.

The gearbox of the invention is due to the design including asuperimposing gear drive, such as for example a bevel gear drive or aplanetary gear drive, which is preferably small and compact and enablesa silent and fast change of the direction of rotation at the firstoutput drive shaft. The silent and fast change of the direction ofrotation is provided by controlling the two motors, wherein a noisy andslow change of gears is avoided. This fast change of the direction ofrotation is advantageous for paste dispensing. The dispensing of highlyviscous material with high torque with the first output drive shaft isstopped, by the following step of a fast change in the direction ofrotation at the first output drive shaft, which prevents furtherundesired dispensing of highly viscous material due to the pressurereduction on the paste material.

The invention is unique and different from prior art systems andadvantageous in various aspects, wherein two motors serve threepurposes. Firstly, high speed is provided by the first motor at thefirst output drive shaft for positioning the plunger in a short time tothe desired position, in both directions, wherein only relatively lowtorque at the first output drive shaft is sufficient. Secondly, lowerspeed but with higher torque is provided by the second motor at thefirst output drive shaft. This is beneficial for driving the plunger orpiston and dispensing the material with high viscosity under highpressure. Finally, a third speed is provided, preferably by the secondmotor at the second output drive shaft, wherein the speed of the seconddrive shaft has a fixed ratio to the speed of the first output driveshaft, when the first output drive shaft is driven with the second motoronly. The third speed is preferable also a low speed for driving themixing element in the mixer only during dispensation of the pastematerial. The fixed ratio of the third speed to the low speed isadvantageous, since the low speed dispenses the material with a specificspeed, and therefore the speed of the mixing tip should be correlated tothis dispensing speed.

In a fourth aspect, the invention relates to a method of mixing andextruding viscous materials comprising the steps of:

-   a) Inserting a cartridge containing one or more viscous materials in    a chamber;-   b) Activating a first motor to move a plunger from a first position    to a second position within the cartridge;-   c) Activating a second motor to move the plunger from the second    position further within the cartridge to dispense the material.

In step c) the plunger is preferably moved toward a third position sothat material is dispensed.

In a fifth aspect, the invention relates to a gearbox, comprising:

-   -   a superimposing gear drive comprising a carrier, a first gear, a        second gear and at least one third gear supported by the        carrier;    -   the second gear being adapted to be driven by a first motor and        the first gear or the carrier being adapted to be driven by a        second motor.

In a sixth aspect, the invention relates to a drive unit comprising:

-   -   a gearbox according to the invention;    -   a first motor and a second motor.

In a seventh aspect, the invention relates to a system for dispensingand/or mixing highly viscous dental products and/or materials comprisinga drive unit as and at least one or more of the following features:

-   -   at least one dispensing cartridge preferably containing a dental        material or a component thereof;    -   at least one plunger adapted to enter an open end of the        cartridge and to expel dental material or a component thereof;    -   a mixing tip for mixing dental material or merging and mixing        components when the dental material or components is/are        expelled from the cartridge;    -   a first drive train for advancing the plunger by the first        output drive shaft;    -   a second drive train for advancing the plunger by the second        output drive shaft; and    -   an electrical or electronic unit for driving and controlling the        system.

In a eighth aspect, the invention relates to a system for dispensingand/or mixing highly viscous dental products and/or materials comprisinga drive unit as and at least one or more of the following features:

-   -   at least one dispensing cartridge preferably containing a dental        material or a component thereof;    -   at least one plunger adapted to enter an open end of the        cartridge and to expel dental material or a component thereof;    -   a mixing tip for mixing dental material or merging and mixing        components when the dental material or components is/are        expelled from the cartridge;    -   a first drive train for advancing the plunger by the first        output drive shaft;    -   a second drive train for driving the mixing tip by the second        output drive shaft; and    -   an electrical or electronic unit for driving and controlling the        system.

In an ninth aspect, the invention relates to the use of a gearbox, asystem and/or a method according to the invention, for dispensing and/ormixing highly viscous dental products and/or materials.

Further preferred features and embodiments of the invention aredescribed in the claims.

It may be provided that the second motor is activated before or when theplunger reaches the second position. Preferably, both motors may work atthe same time and can further start and/or stop independently from eachother.

It may be provided that the first motor is deactivated when the plungerreaches the second position.

It may be provided that the first position is a position in which thecartridge can be inserted in and/or removed from the chamber.

It may be provided that the second position is a position in which theplunger contacts the material.

It may be provided that the method comprises the step that the load ofthe first motor is monitored to detect whether the plunger has reachedthe second position. With this information the steps of activating thesecond motor and/or deactivating the first motor may be automated.

It may be provided that the method comprises the step that when thedispensing is completed the second motor is deactivated.

It may be provided that the method comprises the step that the secondmotor is deactivated to stop the dispensing after material has beendispensed, e.g. a given amount which has been initially set by a user.

It may be provided that the method comprises the step that when thedispensing is completed the first motor and/or second motor is activatedin opposite directions. This activation results in a back movement ofthe plungers and may last for a given time, e.g. 1 second so as toremove the pressure on the components in the cartridge, or until theplungers reach the first position, e.g. for cartridge replacement.

It may be provided that the second motor may be used for mixing thematerial.

It may be provided that the gearbox comprises a first output driveshaft, wherein said first output drive shaft is connected either to thecarrier when the first gear is adapted to be driven by the second motor,or to the first gear when the carrier is adapted to be driven by thesecond motor.

It may be provided that the gearbox comprises a second output driveshaft. Preferably the second output drive shaft is adapted to beconnected to a mixing tip.

It may be provided that the gearbox is adapted that the first motor andthe second motor, when attached to the gearbox, can drive the firstoutput drive shaft.

It may be provided that the gearbox is adapted to drive the first outputdrive shaft with a higher torque when be driven with the second motorthan when be driven with the first motor.

It may be provided that the gearbox is adapted to drive the first outputdrive shaft with higher revolutions per minute when be driven with thefirst motor than when be driven with the second motor.

It may be provided that the gearbox is adapted to drive the first outputdrive shaft by the first motor and the second motor at the same time.

It may be provided that the gearbox is adapted that the speed of thefirst output drive shaft is the sum of the product of the speed providedby the first motor and a first transmission ratio and of the product ofthe speed provided by the second motor and a second transmission ratio.The first and second transmission ratios are defined by the particularconstruction of the gearbox and its gearwheels, and the firsttransmission ratio is the ratio between the speeds of the first outputdrive shaft and the first motor with the second motor standing still,and the second transmission ratio is the ratio between the speeds of thefirst output drive shaft and the second motor with the first motorstanding still.

It may be provided that the gearbox is adapted that when the firstoutput drive shaft is driven by the first motor and the second motor atthe same time, the speed of the first output drive shaft is dominated bythe first motor and high speed is applied to said first output driveshaft. This may occur for example if the plungers are positioned withlow resistance so that the load on the motors is low.

It may be provided that the gearbox is adapted that when the firstoutput drive shaft is driven by the first motor and the second motor atthe same time, the speed of the first output drive shaft is dominated bythe second motor and high torque is applied to said first output driveshaft. This may occur for example if the plungers are pressed againstthe components in the cartridge so that the load on the motors is high.

It may be provided that the second output drive shaft has a fixed speedratio relative to the first output drive shaft and/or relative to thesecond motor.

It may be provided that the first output drive shaft is adapted formoving a plunger.

It may be provided that the second output drive shaft is adapted fordispensing highly viscous material with higher torque at the firstoutput drive shaft followed by the fast change of the direction ofrotation at the first output drive shaft so that further undesireddispensing of highly viscous material is prevented.

It may be provided that the gearbox is adapted that the speed ratio atthe first output drive shaft between driving said output drive shaftwith the first motor only and driving said output drive shaft with thesecond motor only, is preferably in the range of 30 to 200, morepreferably in the range of 50 to 150, more preferably in the range of 80to 120, and more preferably 100.

It may be provided that the gearbox is adapted that the second outputdrive shaft rotates only when the second motor is rotating.

It may be provided that the gearbox is adapted that the first outputdrive shaft is for moving a piston with high speed.

It may be provided that the superimposing gear drive is one of the groupof a bevel gear drive, a differential gear drive and a planetary geardrive.

It may be provided that the gearbox is for carrying out the methodaccording to the invention and/or for dispensing and/or mixing highlyviscous dental materials.

It may be provided that the drive unit is adapted to provide at thefirst output drive shaft a torque in the range of 0.5 to 10 Nm, morepreferably in the range of 5 to 10 Nm, and more preferably in the rangeof 8 to 10 Nm.

It may be provided that the drive unit and gearbox is adapted to provideat the second output drive shaft 200 to 700 revolutions per minute. Itmay be provided that the gearbox, drive unit or system comprises asensor that produces a signal when the plunger reaches the secondposition.

It may be provided that the gearbox, drive unit or system comprises:

-   -   a sensor that monitors the speed of the first output drive shaft        and/or the speed of the first motor;    -   a control unit that is connected to the sensor and produces a        signal when the speed reaches a given minimal value and/or        decreases faster than a given rate.

It may be provided that the gearbox, drive unit or system comprises:

-   -   a sensor that monitors the current feed to the first motor;    -   a control unit that is connected to the sensor and produces a        signal when the current reaches a given maximal value and/or        increases faster than a given rate.

The control unit may be connected to the first and/or second motor, andthe signal produced by the control unit may deactivate the first motorand/or activate the second motor.

It may be provided that the gearbox, drive unit or system comprises aswitch connected to the control unit, wherein:

-   -   when the switch is in a first mode the first output drive shaft        is driven with the high speed to move the plunger from the first        position to the second position and from the second position        further within the cartridge preferably toward a third position        and the material is dispensed; and    -   when the switch is in a second mode the dispensing is stopped        and/or the first output drive shaft is driven in opposite        direction with the high speed to move the plunger back for a        given time or distance or toward the second position.

It may be provided that when the switch is in a third mode the firstoutput drive shaft is driven with the high speed to move the plungertoward the second position.

The switch may be a push switch that is in the first mode when pushed,in the second mode when released, and in the third mode when pushed twotimes in a given period. The switch may also be a slide or a rotaryswitch that has three switching positions for the three modes.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described in more detailbelow with reference to the attached drawings, which are by way ofexample only.

FIG. 1 is a perspective view of a drive unit comprising a gearboxaccording to a first embodiment;

FIG. 2 is a cross-sectional view of the gearbox of the drive unit ofFIG. 1;

FIG. 3 is a cross-sectional view of a gearbox according to a secondembodiment;

FIG. 4 is a perspective view into the gearbox of the drive unit of FIGS.1 and 2;

FIG. 5 is a perspective view of a dispensing device with a gearboxaccording to the present invention; and

FIG. 6 is a schematic side view of the dispensing device according toFIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Examples of drive units constructed in accordance with the principles ofthe invention are illustrated in FIGS. 1 to 4. Each of the shown driveunits comprises a first motor 1, a second motor 2, a gearbox 42, and afirst output drive shaft 10. As can be seen in FIGS. 2 and 3, thegearbox 42 is a superimposing gear drive comprising at least one firstgear 3, 3′, at least one second gear 5, 5′, at least one third gear 4,4′, and a carrier 6 carrying the third gears 4, 4′.

FIGS. 2 and 4 show a first embodiment of a drive unit where thesuperimposing gear drive is a planetary gear drive. In this case, theabove mentioned first, second and third gears correspond to a sun orinner gear 3, a annular or outer gear 5 and a planetary gear 4,respectively.

As shown in FIG. 2, in this first embodiment, the gearbox 42 furthercomprises a second output drive shaft 20 that is connected to the secondmotor 2 via a gear 11. The second output drive shaft 20 is further inconnection to the inner gear 3. Thus, the inner gear 3 is driven by thesecond motor 2, providing by a suitable second transmission ratio hightorque at the first output drive shaft 10. The first output drive shaft10 is connectable directly or via a moving means (not shown), to atleast one plunger (not shown) for advancing a piston (not shown) in acartridge 35 (FIG. 5), or for driving the plunger in reverse directiontoward a back position. The high torque is necessary at the plunger tosupply sufficient force to extrude the highly viscous materials throughan outlet opening of the cartridge. For example, the force required toextrude a material with medium viscosity in the field of dentalmaterials, such as 3M™ ESPE™ Position™ Penta™ Quick Vinyl PolysiloxanePreliminary Impression Material (3M ESPE™ order no. 29063) isapproximately 1500 Newtons (N) for a standard dispensing speed of 22.5mm/min. A force may be provided between about 800 N and about 7000 Ndepending on the preferred dispensing speeds between 22.5 mm/min and 45mm/min and the material to be extruded. For most of the common dentalmaterials the required force is between 1000 N and 3000 N for dispensingspeeds between 22.5 mm/min and 45 mm/min.

The first motor 1 is connected to the annular gear 5 and provides, dueto a suitable first transmission ratio, much higher revolutions perminute, as compared with the second motor 2, at the first output driveshaft 10 for moving the plunger fast forward or backward into a desiredposition. A high speed of the first output drive shaft 10 isadvantageous, for instance after the cartridge has been exhausted andthe plunger has to be moved toward a first or a back position. Afterreplacing the used cartridge with a new cartridge, the plunger is drivenwith high speed toward a second or an initial position, in which theplunger is preferably in contact with the highly viscous material.

For the dispensing operation of the refilled highly viscous material,the gearbox 42 is switched from the first motor 1 to the second motor 2and provides the desired high torque for dispensing the highly viscouspastes or other materials.

Furthermore, it is possible to drive the first output drive shaft 10with both motors 1, 2 at the same time. The resulting speed at the firstoutput drive shaft 10 is the sum of the two speeds each multiplied bythe respective transmission ratio, wherein different driving directionshave different algebraic signs as is known in the art. It is thereforepossible to drive the plunger with high speed, meaning high revolutionsper minute at the first output drive shaft 10, with the two motors atthe same time from the back position toward the initial position inwhich the plunger contacts the highly viscous material. During this fastadvancement of the plunger, the sum of the two speeds provided by thefirst and second motors 1, 2, is dominated by the first motor 1. Whenthe plunger contacts the component, the resistance and therefore theload for both motors 1, 2 increases, but the first motor 1 is less ableto handle the increase. This results in an increasing current of thefirst motor 1 which can be detected by a sensor. The first motor 1 maythen be switched off, and the slower advancing speed of the plunger isprovided exclusively by the second motor 2. Since the second motor 2 wasalready running when the first motor 1 is switched off, the high-speedpositioning movement of the plunger is not interrupted promptly, butslows down smoothly to the low-speed, high-torque dispensing movementprovided by the second motor 2. This results in what might be termed a“phased-out” decrease in speed, or in the reverse situation a“phased-in” increase in speed of the output shaft.

Since the first output drive shaft 10 provides a higher torque whendriven with the second motor 2 than when driven with the first motor 1,the plunger is advanced slowly with high torque and dispenses the highlyviscous material out of the cartridge. Furthermore, since the secondoutput drive shaft 20 is connected to the second motor 2 with a fixedratio, the second output drive shaft 20 rotates only when the secondmotor 2 runs. The output amount of dispensed material is proportional tothe advancing speed of the plunger, and therefore to the rotationalspeed of the first output drive shaft 10. The mixing speed of the mixingtip 30 (FIG. 5), which is connected to the second output drive shaft 20,is therefore automatically adjusted to the dispensing speed due to thefixed ratio between the second output drive shaft 20 and the secondmotor 2, when the first motor 1 is switched off.

FIG. 3 shows a second embodiment of a drive unit where the superimposinggear drive is a bevel gear drive. In this case, the above-mentionedfirst, second and third gears are depicted by numerals 3′, 5′ and 4′,respectively.

In this second embodiment, the first motor 1 again drives the secondgear 5′ whereas the second motor 2 drives the carrier 6. The first gear3′ is connected to the first output drive shaft 10 and has a similarsize and design like the second gear 5′ due to the bevel gear design.

According to the above and other embodiments of the invention, there isno changing of gears needed to accomplish a large speed ratio or range,i.e. the ratio or range between the high speed and the low speed, at anoutput drive shaft 10, which is preferable for a dispensing plungerproviding either a fast positioning velocity or a high torque fordispensing. This results in less noise, highly reliable mechanics andminimal processing time.

FIG. 4 shows a perspective view into a gearbox of the drive unitsuitable for a dispensing device as illustrated in FIGS. 5 and 6. Thedispensing device shown in FIGS. 5 and 6 comprises cartridges which areadapted to receive a quantity of a composition or material to bedispensed. The dispensing device has at least one cartridge 35. In theembodiment according to FIGS. 5 and 6 a first cartridge 35 is visibleonly. A second cartridge is located behind the first cartridge 35 andcan be dimensioned smaller than the first one, depending on the natureof the components. This type of dispensing device comprises two plungersthat are advanced by the drive unit. In FIGS. 5 and 6 a first plunger 40for the first cartridge 35 is visible only. The first plunger 40 isreceived in an open end of the first cartridge 35 and can bear against apiston 41 within the cartridge (shown in FIG. 6). As the plunger 40 isadvanced to move the piston, the piston expels a quantity of materialthrough a front outlet opening of the cartridge.

The plunger 40 can be advanced by the first output drive shaft 10 and bya first drive train. The drive train can comprise gears and sprockets12-15, a pulling device 16, 17, such as guide rails 16 for guidingchains 17, and a support 18 for the plunger 40. In particular, a firstbevel gear 12 can be arranged on the first output drive shaft whichmeshes with a second bevel gear 13 in order to drive a sprocket shaft 14with at least one sprocket. Preferably a first sprocket 15 and a secondsprocket 15′ are provided on both sides as shown in FIG. 5 in order toprovide a more uniform movement of support 18 by driving or moving afirst chain 17 and a second chain (not shown) being linked on both sidesof the support 18. The chains can be guided in a guide rail and furtherby idle sprockets. Any other driving train being able to transfer themovement from the first output drive shaft 10 for axially moving theplunger 40, such as a gear and a gear rod, can also be used.

The plunger 40 can be further advanced by the second output drive shaft20 with a second drive train. The second drive train can comprise adriving belt 22 driven by a first pulley 21 which is attached to thesecond output drive shaft 20. The belt 22 can drive a second pulley 23rotating a pulley shaft 24 advancing the first plunger 40, e.g. by ascrew arrangement between the pulley shaft 24 and a plunger drivingshaft within the plunger support 18 which is connected to the plunger 40(not shown). Preferably the arrangement is such that the plunger 40 doesnot rotate when being axially advanced by the second output drive shaft20. This can be realized by a structure preventing rotation of theplunger driving shaft but allowing an axial movement, such as a tongueand groove structure between the plunger driving shaft and the support18. Any other driving train being able to transfer the movement from thesecond output drive shaft 20 for axially moving the plunger 40, such asa plurality of gears or a gear and a gear rod, can also be used.

The embodiment of the dispensing device shown in FIG. 5 comprises twocartridges for mixing and dispensing dental compositions of twocomponents. These two components are expelled from their respectivecartridges 35 out into a mixing tip 30 where the required dentalmaterial is mixed. The mixing tip 30 can be dynamic and may be coupledto the second drive shaft 20 of the gear box for rotating an inner bodyof the mixing tip 30.

The second drive train 21-24 can drive the dynamic mixing tip 30 with arotating screw inside the tip transporting and further mixing two or inother embodiments more components being expelled from the differentcartridges. The driving can be realized by a tip rotating shaft (notshown) being driven by the pulley shaft 24 and a gear arrangementbetween the pulley shaft and the tip rotating shaft. The gear ratio ofthis gear arrangement can be adapted to correspond to the differentamounts of components being expelled by the cartridges and then mergedin the mixing tip 30.

Preferably the first drive train 12-17 and the second drive train 21-24are arranged to operate independently from each other as in theembodiment shown in FIGS. 5 and 6. However, a driving train can also beprovided superimposing the movements of the first output drive shaft 10and the second output drive shaft 20.

The gearbox used in a suitable device allows a dentist to fill a traywith for example dental impression material in a significantly reducedamount of time, enhancing the benefit to the dentist combined withautomated and fast cartridge exchange.

The invention has now been described with reference to severalembodiments thereof. It will be apparent to those skilled in the artthat many changes can be made in the embodiments described withoutdeparting from the scope of the invention. Thus the scope of theinvention should not be limited to the structures described in thisapplication, but only by structures described by the language of theclaims and the equivalents of those structures.

1. A method of mixing and dispensing viscous materials, comprising the steps of: a) Inserting a cartridge containing one or more viscous materials in a chamber; b) Activating a first motor to move a plunger via an output drive shaft from a first position to a second position within the cartridge; c) Activating a second motor to move the plunger via said output drive shaft from the second position further within the cartridge to dispense the material, wherein the speed of said output drive shaft is the sum or the difference of the driving speed of the first motor and the second motor.
 2. Method according to claim 1, wherein the second motor is activated before or when the plunger reaches the second position.
 3. (canceled)
 4. Method according to claim 1, wherein the first motor is deactivated before or when the plunger reaches the second position.
 5. Method according to claim 1, wherein the first position is a position in which the cartridge can be inserted in and/or removed from the chamber, and the second position is a position in which the plunger contacts the material.
 6. (canceled)
 7. Method according to claim 1, comprising the step of monitoring the load of the first motor to detect whether the plunger has reached the second position.
 8. (canceled)
 9. Method according to claim 1, comprising the step of deactivating the second motor to stop the dispensing.
 10. Method according to claim 1, comprising the step activating the first motor and/or second motor in opposite directions when the dispensing is completed.
 11. Method according to claim 1, wherein the second motor is used for mixing the material.
 12. A gearbox which is adapted to be driven by at least a first motor and a second motor and which comprises at least a first output drive shaft, wherein the gearbox is adapted to drive the first output drive shaft with a higher torque when driven with the second motor than when driven with the first motor and adapted to drive the first output drive shaft with a higher speed or more revolutions per minute when driven with the first motor than when driven with the second motor, wherein the speed of the first output drive shaft is the sum or difference of the first motor and the second motor.
 13. Gearbox according to claim 12 comprising. a superimposing gear drive comprising a carrier, a first gear, a second gear and at least one third gear supported by the carrier; the second gear being adapted to be driven by a first motor and the first gear or the carrier being adapted to be driven by a second motor.
 14. Gearbox according to claim 12, comprising a first output drive shaft, wherein said first output drive shaft is connected either to the carrier when the first gear is adapted to be driven by the second motor, or to the first gear when the carrier is adapted to be driven by the second motor.
 15. Gearbox according to claim 12, further comprising a second output drive shaft.
 16. Gearbox according to claim 12, wherein the second output drive shaft is adapted to be connected to a mixing tip.
 17. Gearbox according to claim 12, wherein the gearbox is adapted such that the first motor and the second motor drive the first output drive shaft.
 18. Gearbox according to claim 12, wherein the gearbox is adapted that the first motor and the second motor can drive the first output shaft at the same time, and wherein the speed of the first output drive shaft is the sum of (a) the product of the speed of the first motor and a first transmission ratio; and (b) the product of the speed of the second motor and a second transmission ratio.
 19. (canceled)
 20. Gearbox according to claim 12, wherein when the first output drive shaft is driven by the first motor and the second motor at the same time, the speed of the first output drive shaft is provided predominantly by the first motor.
 21. Gearbox according to claim 12, wherein when the first output drive shaft is driven by the first motor and the second motor at the same time, the speed of the first output drive shaft is provided predominantly by the second motor.
 22. Gearbox according to claim 12, wherein the second output drive shaft has a fixed speed ratio relative to the first output drive shaft.
 23. (canceled)
 24. Gearbox according to claim 12, wherein the first output drive shaft is adapted for moving a plunger, and the second output drive shaft has a fixes speed ratio relative to the second motor.
 25. Gearbox according to claim 12, wherein the gearbox is adapted for dispensing highly viscous material with higher torque at the first output drive shaft, followed by the fast change of the direction of rotation at the first output drive shaft so that further dispensation of highly viscous material is prevented.
 26. Gearbox according to claim 12, wherein the speed ratio at the first output drive shalt between driving said output drive shaft with the first motor only and driving said output drive shaft with the second motor only, is preferably from 30-200, and more preferably
 100. 27. Gearbox according to claim 12, wherein the second output drive shaft rotates only when the second motor is rotating.
 28. Gearbox according to claim 12, wherein the first output drive shaft is for moving a piston with high speed.
 29. Gearbox according to claim 12, wherein the superimposing gear drive is one of the group of a bevel gear drive, a differential gear drive and a planetary gear drive.
 30. (canceled)
 31. A drive unit comprising: a gear box according to claim 12; and a first motor and a second motor. 32-33. (canceled)
 34. System for dispensing and/or mixing highly viscous dental products and/or materials, comprising: a drive unit according to claim 31, and at least one of the following features: at least one dispensing cartridge preferably containing a dental material or a component thereof; at least one plunger adapted to enter an open end of the cartridge and to expel dental material or a component thereof; a mixing tip for mixing dental material or merging and mixing components when the dental material or components is/are expelled from the cartridge(s); a first drive train for advancing the plunger by the first output drive shaft; a second drive train for advancing the plunger by the second output drive shaft; and an electrical drive unit for driving and controlling the system.
 35. System for dispensing and/or mixing highly viscous dental products and/or materials, comprising: a drive unit according to claim 31, and at least one of the following features: at least one dispensing cartridge preferably containing a dental material or a component thereof; at least one plunger adapted to enter an open end of the cartridge and to expel dental material or a component thereof; a mixing tip for mixing dental material or merging and mixing components when the dental material or components is/are expelled from the cartridge(s); a first drive train for advancing the plunger by the first output drive shaft; a second drive train for driving the mixing tip by the second output drive shaft; and an electrical drive unit for driving and controlling the system. 36-42. (canceled) 